Apache Syncope offers the ability to extend / customize the base behavior on every deployment by allowing to provide custom implementations of a few Java interfaces; such implementations can be provided either as Java or Groovy classes, with the latter being particularly attractive as the machinery is set for runtime reload.
Such a feature has been available for a while, but recently it was discovered that a malicious administrator can inject Groovy code that can be executed remotely by a running Apache Syncope Core instance.
Users are recommended to upgrade to version 3.0.14 / 4.0.2, which fix this issue by forcing the Groovy code to run in a sandbox.